= Diamond anvil culet
{title2=$A_c=\pi d_c^2/4$}
A <diamond anvil culet> is the small flat contact face at the tip of a <diamond> anvil. Its diameter $d_c$ determines its nominal <surface area> $A_c$. The <gasket> hole has a different <surface area> $A_h$; neither should be confused with the much larger drive mechanism. For an ideal static axial balance, $F$ is the compressive <force> on either anvil. The two equal opposing loads do not produce $2F$ through a single contact.
For an original chosen geometry, $F=1000\,\mathrm N$ and $d_c=0.300\,\mathrm{mm}$ give
$$
A_c=7.0686\times10^{-8}\,\mathrm{m^2},\qquad
\bar q=F/A_c=14.147\,\mathrm{GPa}.
$$
Here $\bar q$ is the mean axial contact <stress> over the culet, not a measured chamber <pressure>. Using a $0.100\,\mathrm{mm}$ hole instead would give $F/A_h=127.324\,\mathrm{GPa}$, nine times larger. That substitution falsely assigns the entire applied <force> to the hole.
To see the missing load path, idealize the culet as a coplanar hole region plus a surrounding contact annulus. With a hydrostatic chamber <pressure> $p$ and axial resultant $F_g$ carried by the <gasket>, its <force> balance is
$$
F=pA_h+F_g.
$$
If the stipulated chamber <pressure> is $5.40\,\mathrm{GPa}$, the hole carries only $42.4\,\mathrm N$ and the <gasket> carries $957.6\,\mathrm N$. These are model loads, not measurements. Real <gasket> deformation and anvil <elasticity> alter the local contact <stress>; the scalar balance cannot predict $p$ without additional information. This is why internal <pressure calibration> matters even when applied <force> is accurately known.
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